1. Field of the Invention
The present invention relates to a projection display device (a projection type image display device, such as a transmission type liquid crystal projector or a reflection type liquid crystal projector) and an image projection system using the same. Further, the present invention relates to a light source for use in a projection display device, and more particularly to the cooling of the light source of a projection display device.
2. Related Background Art
Conventionally, as the light source lamp of a projection type image display device, there has been used a discharge lamp, such as a metal halide lamp, a high pressure mercury lamp, a halogen lamp, or a xenon lamp; in all of them, the lamp itself must be cooled when mounted in the display device. As the cooling method, air cooling is generally adopted. That is, the lamp is cooled by utilizing airflow generated by an axial fan, a sirocco fan, or the like, the air used being dissipated into the exterior of the device.
The main purposes of this lamp cooling are: (1) to maintain the light emission efficiency of the lamp light emission tube and prevent a deterioration thereof; and (2) to cool the lamp reflector itself and reduce the radiation heat from the lamp reflector surface before discharging it to the exterior of the device.
As a result of the recent reduction in device size, or from the viewpoint of optical construction, an optical member (inclusive of a projection lens) is often arranged close to the lamp. Japanese Patent Application Laid-Open No. 2000-221599 discloses a construction in which a lamp light emission tube is intensively cooled by a fan provided between the lamp and the projection lens, and the lamp reflector itself is cooled by utilizing the suction force of an exhaust fan provided on the opposite side, with radiation heat from the lamp reflector surface being reduced before being discharged to the exterior of the device.
Japanese Patent Application Laid-Open No. 2003-131166 discloses, as an embodiment, a construction in which a cooling fan is provided in the gap between the lamp and the projection lens or the color separation/composition optical system.
However, in the construction as disclosed in Japanese Patent Application Laid-Open No. 2000-221599, the fan provided between the lamp-and the projection lens serves to intensively cool the light emission tube of the lamp, and the cooling of the lamp reflector is effected by utilizing the suction force of the exhaust fan provided on the opposite side. In this construction, when the heat generation amount of the lamp itself is very large, the cooling of the lamp reflector is not effected sufficiently, with the result that the lamp reflector surface attains high temperature. Then, radiation heat from the lamp reflector surface is conducted around the fan for cooling the light emission tube of the lamp, and there is the possibility of the component (the projection lens) close to the lamp reflector surface being heated to high temperature.
Here, when the component close to the lamp reflector surface is the projection lens, and this projection lens is formed of plastic, or the projection lens barrel itself is formed of plastic, there are involved various cases of deterioration in image projection performance due to variation in aberration caused by temperature change, a deterioration in imaging performance, a change in inter-lens distance caused by expansion/contraction of the lens barrel, mutual offset of the lenses, a deterioration in optical performance caused by inclination, etc.
Also in the case in which the component close to the lamp reflector surface is a polarization beam splitter constituting the optical elements, the polarization beam splitter itself generates heat due to the radiation heat of the lamp; in particular, when the volume of the polarization beam splitter itself is large, a temperature distribution is generated in the prism. When such a temperature distribution is generated, inner stress is generated in the optical material itself, with the result that there is generated birefringence due to the linear polarization of the incident light becoming elliptical polarization because of the elasticity of light, that is, the relationship between reflection and transmission is disturbed (Reflection and transmission cease to be effected reliably due to the generation of an undesirable polarization component), with the result that leakage light is allowed to reach the projection surface to thereby cause a deterioration in contrast, making it impossible to obtain a high-quality projection type image display device.
Similarly, in the case in which the component close to the lamp reflector surface is a liquid crystal panel (image forming element) constituting the display portion of the projection type image display device, the liquid crystal panel itself generates heat due to the lamp radiation heat; a liquid crystal is inherently easily affected by heat, and a deterioration in contrast, color heterogeneity, etc. are generated due to vaporization of the liquid crystal itself, making it impossible to obtain a high quality projection type image display device.
On the other hand, if the lamp itself is cooled by a cooling fan, due to heat radiation from the lamp, the components around the lamp (the lamp case, the lamp cover, etc.) attain high temperature as is well known in the art. In view of this, it is general practice to form the components around the lamp of a plastic material capable of withstanding the lamp radiation heat, such as PPS resin or unsaturated polyester. However, such a plastic material has low heat conductivity and high heat radiation rate, so that, when the components around the lamp once attain high temperature, it is very difficult to cool them due to their low heat conductivity; moreover, due to their high heat radiation rate, heat is allowed to fill the interior of the device, resulting in a deterioration in the cooling efficiency for the other portions in the device requiring cooling.
In view of this, it is general practice to set the air quantity and air flow rate of the fan for cooling the lamp so as to keep, as much as possible, the components around the lamp from attaining high temperature. However, it is impossible to sufficiently prevent the components around the lamp from attaining high temperature solely by adjusting the airflow from the cooling fan. In this regard, Japanese Patent Application Laid-Open No. 2002-244210 discloses a method according to which a heat shield plate is provided between the lamp and a component around the same (the lamp cover), thereby preventing the component around the lamp (the lamp cover) from attaining high temperature due to the radiation heat from the lamp.
Further, Japanese Patent Application Laid-Open No. 2003-29342 discloses a method according to which there is arranged a heat dissipating plate (a lamp shade) so as to surround the reflector portion of the lamp.
As a means for meeting the recent demand for an increase in the brightness of a projection type image display device, the lamp output is increased. This, however, involves an unexpectedly large lamp heat generation amount, that is, a great increase in lamp radiation heat amount. Thus, the heat dissipation achieved by the provision of a heat shield plate in the gap between the lamp and the component around the same (the lamp cover) as disclosed in Japanese Patent Application Laid-Open No. 2002-244210, cannot keep up with this large increase in lamp heat radiation amount, and thermal saturation of the heat shield plate itself is to be expected.
As a result, the component around the lamp (the lamp cover) is allowed to attain high temperature this time due to the radiation heat of the heat shield plate itself, so that, as in the prior art, heat fills the interior of the device. Thus, not only is the cooling efficiency for the other portions in the device requiring cooling deteriorated, but, at worst, the component around the lamp (the lamp cover) cannot withstand the heat and may suffer material damage.
In the construction as disclosed in Japanese Patent Application Laid-Open No. 2002-244210, it might be possible to prevent the component around the lamp (the lamp cover) from attaining high temperature by using a plurality of heat shield plates. However, provision of a plurality of heat shield plates would result in a product that is inadequate in terms of cost and space saving.
Further, the fact that the component around the lamp attains high temperature means that the exterior case covering that component also attains high temperature due to the radiation heat from the component. Thus, this is likely to result in a product not only rather uncomfortable for the user of the projection type image display device during operation due to the heat of the exterior case, but also undesirable from the viewpoint of product safety.
Apart from this, it might be possible to cool the component around the lamp by increasing the air quantity and air flow rate of the cooling fan. That, however, would lead to an increase in the noise due to the increase in the fan RPM and to an increase in the size of the cooling fan, which is undesirable from the viewpoint of the recent demand for a reduction in the noise and size of a projection type image display device.